The numerical control apparatus performs a numerical control processing based on a processing program registered in memory or externally input via the tape, communication or FLD (floppy disk), and drives the machine tool in accordance with the processing result to machine a workpiece. This numerical control apparatus has the feature that performs the skip function.
This skip function is effected upon a command from the processing program such asG31 Xx Yy Zz Ff;(X, Y, Z: axial addresses, x, y, z: coordinate values, Ff: feed speed command). If a skip signal is entered from the outside during the linear interpolation by the G31 command, the machine feed is promptly stopped to discard the residual distance, and the next block is executed.
By the way, in the case where a plurality of skip signals (external signals) are provided, and every time a skip signal is input into the numerical control apparatus, the tool is moved to the final specified position by decreasing stepwise, or increasing or decreasing stepwise the speed, the skip function is employed.
However, the conventional numerical control apparatus could only perform a skip command in which one block can deal with one skip signal. Therefore, in the case where a plurality of skip signals were provided, and every time a skip signal (external signal) was input into the numerical control apparatus, it was desired to decrease stepwise, or increase or decrease stepwise the speed, it was required to divide the skip command into the blocks desired to change the speed, in which the skip command was issued for each block.
In this case, because of the necessity of dividing the skip command into the blocks desired to change the speed, to effectuate the skip signal, it was required that a movement distance is calculated in advance to be included within its signal range (skip signal interval), and the skip command is issued in the movement range.
Therefore, in the case where it was desired to decrease stepwise, or increase or decrease stepwise the speed, every time the skip signal (external signal) is input into the numerical control apparatus, it took much labor to fabricate the processing program.
Also, if the skip signal is input, the residual distance for the block is canceled, so that the speed becomes “0”. Therefore, it takes some time to initiate the next block, resulting in a problem that in the case where the tool is moved to the final specified position by decreasing stepwise, or increasing or decreasing stepwise the speed, every time the skip signal (external signal) is input into the numerical control apparatus, it takes a long time.